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encoding/base64: This change modifies Go to take strict option when decoding base64

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If strict option is enabled, when decoding, instead of skip the padding
bits, it will do strict check to enforce they are set to zero.

Fixes #15656

Change-Id: I869fb725a39cc9dde44dbc4ff0046446e7abc642
Reviewed-on: https://go-review.googlesource.com/24964
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Xuyang Kang 2016-07-17 00:23:56 -07:00 committed by Russ Cox
parent 56b5546b91
commit 87b1aaa37c
2 changed files with 42 additions and 3 deletions
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24
src/encoding/base64/base64.go
View file

@ -23,6 +23,7 @@ type Encoding struct {
encode [64]byte
decodeMap [256]byte
padChar rune
strict bool
}
const (
@ -62,6 +63,14 @@ func (enc Encoding) WithPadding(padding rune) *Encoding {
return &enc
}
// Strict creates a new encoding identical to enc except with
// strict decoding enabled. In this mode, the decoder requires that
// trailing padding bits are zero, as described in RFC 4648 section 3.5.
func (enc Encoding) Strict() *Encoding {
enc.strict = true
return &enc
}
// StdEncoding is the standard base64 encoding, as defined in
// RFC 4648.
var StdEncoding = NewEncoding(encodeStd)
@ -311,15 +320,24 @@ func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err error) {
// Convert 4x 6bit source bytes into 3 bytes
val := uint(dbuf[0])<<18 | uint(dbuf[1])<<12 | uint(dbuf[2])<<6 | uint(dbuf[3])
dbuf[2], dbuf[1], dbuf[0] = byte(val>>0), byte(val>>8), byte(val>>16)
switch dlen {
case 4:
dst[2] = byte(val >> 0)
dst[2] = dbuf[2]
dbuf[2] = 0
fallthrough
case 3:
dst[1] = byte(val >> 8)
dst[1] = dbuf[1]
if enc.strict && dbuf[2] != 0 {
return n, end, CorruptInputError(si - 1)
}
dbuf[1] = 0
fallthrough
case 2:
dst[0] = byte(val >> 16)
dst[0] = dbuf[0]
if enc.strict && (dbuf[1] != 0 || dbuf[2] != 0) {
return n, end, CorruptInputError(si - 2)
}
}
dst = dst[dinc:]
n += dlen - 1

21
src/encoding/base64/base64_test.go
View file

@ -85,6 +85,11 @@ var encodingTests = []encodingTest{
{RawStdEncoding, rawRef},
{RawURLEncoding, rawUrlRef},
{funnyEncoding, funnyRef},
{StdEncoding.Strict(), stdRef},
{URLEncoding.Strict(), urlRef},
{RawStdEncoding.Strict(), rawRef},
{RawURLEncoding.Strict(), rawUrlRef},
{funnyEncoding.Strict(), funnyRef},
}
var bigtest = testpair{
@ -436,6 +441,22 @@ func TestDecoderIssue7733(t *testing.T) {
}
}
func TestDecoderIssue15656(t *testing.T) {
_, err := StdEncoding.Strict().DecodeString("WvLTlMrX9NpYDQlEIFlnDB==")
want := CorruptInputError(22)
if !reflect.DeepEqual(want, err) {
t.Errorf("Error = %v; want CorruptInputError(22)", err)
}
_, err = StdEncoding.Strict().DecodeString("WvLTlMrX9NpYDQlEIFlnDA==")
if err != nil {
t.Errorf("Error = %v; want nil", err)
}
_, err = StdEncoding.DecodeString("WvLTlMrX9NpYDQlEIFlnDB==")
if err != nil {
t.Errorf("Error = %v; want nil", err)
}
}
func BenchmarkEncodeToString(b *testing.B) {
data := make([]byte, 8192)
b.SetBytes(int64(len(data)))